PARENT SESSION
Contributed Oral Session 77: Paleoecology
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal
The relative importance of vegetational vs. climatic controls on post-glacial fire regimes in the southern Brooks Range, AK.
Higuera, Philip *,1, Brubaker, Linda1, Anderson, Patricia1, Hu, Feng Sheng2, Clegg, Ben 2, Brown, Tom3, 1 University of Washington, Seattle, WA2 University of Illinois, Urbana, IL3 Lawrence Livermore National Laboratory, Livermore, CA
ABSTRACT- The post-glacial history of vegetation and climate in northern Alaska provides an excellent opportunity to document relationships between changes in vegetation, climate, and fire regimes. Over the past 13 k years at least four distinct vegetation assemblages have existed in the southern Brooks Range, and climate has trended towards cooler and moister conditions after maximum warmth in the early Holocene. We use multiple lake-sediment records to refine vegetation history and, for the first time, reconstruct fire history for the region with macroscopic charcoal stratigraphy. Select sites are used to reconstruct summer temperatures or moisture with fossil chironomids and oxygen isotopes. Our records suggest that frequent fires occurred during late-glacial times, when the region was approximately 3 degrees C cooler than present and dominated by birch shrub tundra. Fire occurrence decreased when vegetation assemblages changed to deciduous forests dominated by Populus, despite evidence of warmer-than-present temperatures. Coincident with a decrease in Populus and the addition of white spruce to the shrub tundra during the early Holocene, charcoal records suggest an increase in fire occurrence. Climate proxies suggest a gradual cooling on the order of 1degree C throughout the Holocene, with moistening around 6-7 k ybp. Despite this trend, the most pronounced change in fire regimes occurred with the addition of black spruce during the mid-Holocene, when both charcoal abundance and peak frequencies increased to maximum levels. Overall, millennial-scale fire history was more strongly linked to changes in vegetation than to changes in climate. These results suggest that vegetation assemblages (i.e. fuels) play an important role in mediating the effects of climatic change on fire regimes. Simple climate-fire relationships cannot, therefore, be extrapolated to predict the response of fire regimes to climatic change without considering patterns of vegetation change.
Key words: fire history, vegetation change, climate change, northern Alaska